Coupling transformer for radio systems



. R. S. PIPER. COUPLING TRANSFORMER FOR RADIO SYSTEMS.

APPLICATION FILED JUNE 15, 1922.

,1 W S 2. F mm mm mmf .5 DH 4 NM t 7 m F M mm R. s. PIPER. COUPLING.TRANSFORMER FOR RADIO SYSTEMS.

' APPLICATION FILE-D JUNE 15', I922- Patented D0012, 1922.

2 SHEETSSHEET 2.

Patented Dec. 1 2, 1922.

UNITED ST TES PATENT OFFICE.

RALPH S. PIPER, OF CH ICAGO, ILLINOIS.

COUPLING TRANSFORMER FOR RADIO SYSTEMS.

, Application filed June15, 1922. Serial No. 56 8,5 18.

tween the antenna circuit and the oscillation circuit of the detector tube which is commonly used in such circuit. The amounts or quantities of energy concerned in the operation of such circuits is almost infinitesimal and one purpose of this invention is to conserve all of the energy possible and present it to the input circuit with the least pos sible loss.

It is well known that the best possible conditions for energy transference from one circuit to another through a magnetic coupling of the same, requires the use of a tight or, close coupling. All low frequency commercial power circuits are coupled in consonance with this principle; but in the case of wireless reception circuits, which'of course, are of very high frequencies, the in put circuit is concerned notalone with energy transference but must discharge other functions, such as detection and amplification, and accordingly a compromise must be made between a close coupling which would give the maximum power transference and a more or less loose couplin which has sufiicient elasticity and flexibi ity t5 permit of attainment of resonance between the several circuits involved. l

As far as I am aware, it has been the 'prac tice heretofore, to extend this loose coupling characteristic throughout the range of the coupling. Usuall the coupling circuits are vmade movable with respect to eachother,

and hence no part of the circuits can be said to have a strictly close coupling.

I have discovered, that it is possible to divide the coupling into sections, or portions, some of which may be as closely coupled as in ordinary power transformer eircults and that the functions of a loose coupling may be relegated to .certain other portions of'the winding which present a decided loose coupling characteristic. The result of this arrangement is, that the tight coupling portions will give exceptionally good energy transference and there will yet be sufiicient flexibility in the coupling as a whole, to permit of the establishment of resonance relation u onwhich the efficient operation of a reception set is conditioned as regards detection and amplification.

As is well understood, when the antenna circuit is tuned to the passing radio waves,

oscillations are set up in the antenna circuit and these oscillations induce oscillations which cause. alternating currents to flow in the secondary-circuit. If the secondary circuit is put in resonance with the primary antenna circuit, these secondary oscillations will be of maximum strength.

The inductive coupling-between the an-' tenna circuit and'the secondary circuit may be varied without very greatly changing the wave length or oscillation frequency. of either. This inductive coupling may be either close or tight or else it maybe loose or open. Close or tight coupling is secured by bringing the primary and secondary coils into close relation, as by winding the'layers of the two coils'togletherside by side orbyfl winding one over t eother, or by the autotransformer arrangement;'-while loose 01" open coupling is obtained by separating the coils some distance from each other.

When tight cou ling is employed the runtual induction e ect is strong, producing currents of greatly increased strength inthe.

secondary circuit, but rendering the latter exceedingly sensitive and difficult to maintain in proper adjustment of resonance under varying conditions. Loose coupling, on the other hand, greatly improves the tuning qualities or selectivity. Less energy is collected from the antenna circuit and the effective resistances of both circuits are reduced but, necessarily, the signal strength is considerably decreased. g

The purpose of my invention is accordingly to provide an inductive coupling between the antenna circuit and the secondary cirpuit which secures the increased signal strength afforded by a tight or close coupling and at the same time gives the increased tilt selectivity and improved tuning qualities of the loose coupling; 7

Tn the following description I shall refer to the accompanying drawings, in whlch Figure 1 is a perspective View, partly broken away, of a coupling transformer embodying my invention; Fig. 2 is a side elevation, partly broken away of a similar transformer showing a sliding contact for varying the primary turns in circuit and taps connected to a plurality of points in the secondary;'

turns of the wireare threaded. The pri mary coil 14 is then wound upon the tube, lying in close contact with the exposed peripheral portions of the secondary coil wound on sections 10. This construction brings the primary and a portion of the sec-' ondary into close inductive relation forming a tight coupling throughout those portions which overlie the sections 10 of the cylinden, while the intermediate portions 12 of the secondary which extend across the interior from one side of the cylinder to the other are in open inductive relation or loosely coupled with the primary. It will be seen that the loose coupled portions of the secondary, extending between the slots 11, constitute in 'eifect a chord of a circle formed by a section of the cylinder. And it will be noted that as the secondary winding progresses along the chord, the degree of coupling varies. In order to take advantage of this. varying coupling factor, a series of taps are provided, the connections to which may be mechanically varied, as illustrated structurally in Figs. 2, 3 and l, and diagrammatically inFig. 5, and the amount of mutual induction between the coils in the loosel coupled portions will vary, of course,

accor ing to the distance separating the'- coil sections 12 and the primary 14%. The

amount of tight coupling may be chan ed by making-the cylinder sections 102 whic support the secondary, wider or narrower, that 1s, by making the sections 12 extend over a greater or lesser arc of the cylinder. Likewisethe degree of loose coupling can be varied by changing the shape of the tubular support or by varying the relative position of the coils. T have shown a cylindrical supporting tube but it is evident that 1 may iaaaeaa employ an ellipsoidal, polygonal or other suitable shape for the'purpose of obtaining the desired ratio bejgveen the tight and loose coupled portions and to vary the degree of loose coupling and to produce the proper gradation of mutual induction over the.

ondary circuits. 1 have indicated in F ig..7

one of the usual circuit diagrams, the several elements being indicated by the well-known conventions and designated by the reference characters usually applied to them so that they will be recognized by engineers without I further explanation. In this diagram T have endeavored to indicate close and loose coupling between the primary 14 and the secondary 12 by positioning the central part of the secondary close to the primary while the ends of thesecondary taper outwardly therefrom.

- In Fig. 7 the coils of the coupling transformer are not provided with any adjustable connections, the terminals of the primary being connected to the aerial and to ground, and thesecondary terminals being connected to the grid and to the filament of the au dion tube. In this case the tuning is effected by the adjustable condensers c, in the antenna and C in shunt to the terminals of the secondary. In order to increase the range of adjustment I provide means for varying the effective lengths of both primary and secondary coils. One means of accomplishing this is shown in Fig. 2 and diagrammatically in Fig. 5. A sliding contact 15, which may be connected to ground, as indicated in Fig. 5, or to the aerial, may be.

moved along the primary, the insulation being removed from the wires along its path. The secondary is provided at intervals with taps t which are connected to switch contacts 16, over which the switch arm 17 is moved asindicated in Fig. 5. In the diagram of Fig. 5 I have illustrated anotherv known arrangement of circuits in which the head-phone HP is connected to the oscillaed to the aerial and thelother to the ground connection if desired, as indicated diagrammatically in Fig. 6. The sliding contacts 15 may be located over parts of the primary which are not adjacent to the secondary, as

indicated in Fig. 4 so that there is no danger that the slider will contact with the secondl ks will be understood by those familiar with radio systems the antenna circuit is tuned to the incoming waves by adjusting the effective length of the primary 14 and the adjustable condenser 0 and the secondary oscillation circuit is then laced in resonance with the primary circult by adjusting the effective length of the secondary and adjusting the variable condenser C.

It is evident that the antenna circuit is in the best receptive condition for the incoming Waves when the primary is in resonance with the received oscillations. Owing to the inductive relation described above of tight and loose coupled sections, it is believed a reaction is set up between the field of the primary and secondary respective close and loose coupled sections. These sections of each winding are electrically connected in series, and it isbelieved that magnetically there occurs automatically a shift or adjustment in the coupling under different conditions, such that the coupling improves theselectivity according to the requirements of resonance. This automatic change in coupling causes an inherent tendency of my transformer to shift into resonance and to maintain this condition which greatly facilitates obtaining exact conditions of resonance. This is only my supposition based upon actual experience with this apparatus, but I do not wish to be bound by this theory of operation.

While I have illustrated my invention in connection with the usual indirect inductive coupling it is obvious that many advantages thereof apply equally well to the direct inductive coupling, both of which are well known in the art, as explained on pages 267 and 268 of a book entitled The rinciples underlying radio communication (sectems, comprising a primary coil and a secondary coil in fixed relation and of different cross-sectional configuration, the turns of said respective coils having a common area, and each coil having also a spaced area with respect to the other coil.

4. A coupling transformer for radio systems, comprising a primary coil and a secondary coil in fixed relation, certain peripheral sections of the turns of the respective coils being in contiguous superposed relation, and other peripheral sections of the turns of said coils being spaced apart.

5. A coupling transformer for radio systems, comprising a tubular insulating support, a secondary coil wound upon symmetrically disposed peripheral sections of said support, intermediate connecting sections of the secondary passing through slots in the support and across the interior thereof, and a primary coil wound upon the support and superposed upon the exposed peripheral sections of the secondary, whereby said secondary forms a tight magnetic coupling with the primary at said superposed portions and a loose coupling therewith at said intermediate portions.

In testimony whereof I afiix my signature.

RALPH S. PIPER. 

